1. Field of the Invention
The present invention relates to a novel bolt and socket which are designed so that they can be accurately tightened by, for example, an impact wrench.
2. Description of Related Art
Since a conventional hexagon head bolt has a hexagon head, when the hexagon bolt is tightened by an impact wrench, a socket hole 3 is rotated an angle .theta. with respect to a bolt head 1 due to a clearance between the socket hole 3 of the impact wrench and the bolt head 3, as shown by arrows in FIG. 4. The corner portions 2 of the bolt head 1 are respectively inevitably brought into point contact with the inner sides 4 of the socket hole 3. The conventional bolt thus has the fault that this point contact causes damage to the bolt head 1 and thus leads to rusting of the bolt head 1. In the case of a M-6 bolt, the minimum shift angle .theta. is about 0.degree. 14', and the maximum shift angle .theta. is about 4.degree. 13'. These angles are measured with respect to the clearance between the socket hole 3 and the bolt head 1. However, since the clearance between both members is generally actually set to a rather large value in order to facilitate the engagement between the socket hole 3 and the bolt head 1, the shift angle .theta. is generally still larger.